Microfilaments are solid rods made of globular proteins called actin and are common to all eukaryotic cells. Long chains of the molecules are intertwined in a helix to form individual microfilaments. These filaments are primarily structural in function and are an important component of the cytoskeleton, along with microtubules.
In association with myosin, microfilaments help to generate the forces used in cellular contraction and basic cell movements. They enable a dividing cell to pinch off into two cells and are involved in amoeboid movements of certain types of cells. They also enable the contractions of muscle cells.
Information provided by: http://micro.magnet.fsu.edu